The Seacoast United Mariners will compete in the National Premier Soccer League for the 2018 season, as part of the Northeast-Atlantic Division. Teams competing in the 2017 season include the Brooklyn Italians (NY), NY Athletic Club, NY Cosmos, Greater Lowell FC (MA), and the RI Reds (RI). The Seacoast United Mariners are the first NPSL franchise in Maine.

Scheduling for the upcoming season takes place at the Annual General Meeting, typically scheduled during the NSCAA National Convention in January of each year. League play begins in May and generally ends mid-late July, with playoffs for teams that advance. The league wraps up late July/early August, to allow for players to head back to their collegiate programs for preseason.

The NPSL is officially affiliated with the United States Adult Soccer Association (USASA) and qualifies for US Open Cup through USASA channels. The league is generally considered to be the fourth tier of soccer in the United States behind Major League Soccer (MLS), the North American Soccer League (NASL), United Soccer Leagues Professional Division (USL Pro), and roughly equal with the USL Premier Development League (PDL).